Spark plug with improved electrode



Aug 25, 1964 R. .1. VAN DUYNE ETAL, 3,146,370

I SPARK PLUG WITH IMFROVED ELECTRODE Filed June 2l, 1962 l United States Patent O 3,146,370 SPARK PLUG WlTl-I IMPROVED ELECTRODE Robert J. Van Duyne and Robert W. Smith, Flint, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed .lune 21, 1962, Ser. No. 204,105 4 Claims. (Cl. 313-118) This invention relates to spark plugs and has as its Object the provision of a spark plug with an improved longer life electrode.

At the present state of the art, the chief limiting factor on spark plug life is electrode wear and erosion. The ideal electrode would be one of a metal having maximum resistance to wear or erosion from electrical discharge, having maximum resistance to corrosion from the metallic salts and the like which are formed in the combustion chamber from the gasoline additives, and having sufficient mechanical strength to assure against any cracks or ruptures. Unfortunately no such metal is known and those which come closest to meeting these requirements are extremely expensive. Hence, all current spark plug electrode materials constitute compromises, one desirable property being sacrificed to a considerable extent to gain another useful property.

The present invention provides a spark plug electrode which incorporates two different metals the structural combination of which affords an optimum combination of the aforementioned useful properties. In accordance with the invention the electrode consists of an iridium firing tip portion secured to a cobalt supporting structure. Both of these metals are extremely resistant to chemical attack by lead salts and other compounds formed in the combustion chamber. Iridium additionally is extremely resistant to spark erosion; however by itself it is somewhat lacking in mechanical strength. Also, it is quite expensive. The cobalt compensates for these two deciencies in that it has excellent mechanical strength and is comparatively inexpensive. Hence the structural combination of the two metals provides an optimum set of desirable properties.

A specific embodiment of the invention will now be described by reference to the accompanying drawings in which:

FIGURE 1 shows a side view of a spark plug made in accordance with the invention; and

FIGURE 2 is a perspective view of the lower or firing end of the spark plug shown in FIGURE 1.

Referring now to the drawings, the spark plug shown comprises a metal shell 1, insulator Z concentrically secured within the shell, a center electrode 3 which extends from the end of the insulator and is electrically connected to the terminal 4 at the top of the plug, and a ground electrode 5 welded to the end of the shell and extending into spaced spark gap relationship with the end of the center electrode. The structural details of the shell, the

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insulator and the electrical terminal are of no importance to the present invention; these components can be of constructions well known in the art.

In accordance with the invention the center electrode 3 comprises a cobalt wire 6 having an iridium core 7 exposed at the lower or firing tip end thereof. The iridium core is bonded to the cobalt as by welding, swaging or cosintering of the respective metal powders. For lower cost the core need only extend into the Wire a relatively short distance if desired, this as indicated at 8.

The ground electrode 5 consists of a cobalt wire 11, of rectangular section, welded to the shell at 9 and having embedded in and welded, co-sintered from the respective metal powders or otherwise bonded to the upper surface of the firing end thereof a rectangular plate of iridium 19. Hence the sparking surfaces for both electrodes are of iridium and the supporting structure for these firing surfaces consists of cobalt.

It will be understood that While in the spark plug shown and described both the center electrode and the ground electrode embody the invention, the invention can be practiced by incorporating it into only one or the other of these electrodes. Also, while details of the invention have been described specifically with reference to one particular embodiment, it is not so limited since various changes and modifications may be made, all within the full and intended scope of the claims which follow.

We claim:

l. A spark plug comprising a pair of electrodes in spaced spark gap relationship, at least one of said electrodes comprising a body of cobalt having an iridium portion secured thereto at the spark gap.

2. A spark plug comprising a pair of electrodes having end portions in spaced spark gap relationship, at least one of said electrodes comprising a cobalt wire having an iridium insert secured t0 the end portion thereof at the spark gap.

3. A spark plug comprising a pair of electrodes having end portions in spaced spark gap relationship, one of said electrodes comprising a cobalt Wire having at least at the end portion thereof an iridium core forming the sparking surface of said electrode.

4. A spark plug comprising a pair of electrodes having end portions in spaced spark gap relationship, one of said electrodes comprising a cobalt Wire having an iridium plate embedded in and bonded to the end portion thereof, said iridium plate forming the sparking surface of said electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,239,561 Hopps Apr. 22, 1941 3,042,474 Aurand July 3, 1962 FOREIGN PATENTS 526,347 Great Britain Sept. 17, 1940 

1. A SPARK PLUG COMPRISING A PAIR OF ELECTRODES IN SPACED SPARK GAP RELATIONSHIP, AT LEAST ONE OF SAID ELECTRODES COMPRISING A BODY OF COBALT HAVING AN IRIDIUM PORTION SECURED THERETO AT THE SPARK GAP. 